The aircraft rises and falls from 1 to 5 feet while hovering with no input to the transmitter.

CAUSE: Shear pin hole in main shaft has been worn out and enlarged. Usually caused by crashes. Can be checked by testing the play between main shaft and head.

LIKELIHOOD: 2 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Replace main shaft/gear assembly.

DIFFICULTY: 4 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Worn Center Hub and Rotor Head.

LIKELIHOOD: 3 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Replace Center Hub and Rotor Head.

DIFFICULTY: 7 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Worn or damaged servo.

LIKELIHOOD: 4 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Repair or replace the servo.

DIFFICULTY: 6 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: High frequency interference (Glitching).

LIKELIHOOD: 4 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Make sure the antenna is extended all of the way out and pointed away from the helicopter. Check to see if there is any moving/touching metal parts on the helicopter. Try taking the helicopter to a different location.

DIFFICULTY: 1 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Main motor is failing.

LIKELIHOOD: 6 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Replace the Main Motor.

DIFFICULTY: 5 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

While flying and hovering the main rotor wobbles on a horizontal plane. The aircraft is very noticably shaking and is very difficult, if not impossible, to control. This usually appears after a crash or blade strike.

CAUSE: Main blades are out of track.

LIKELIHOOD: 1 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Adjust main rotor blade tracking.

DIFFICULTY: 3 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: The Spindle may be bent. Usually the result of a crash or blade strike.

LIKELIHOOD: 2 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Straighten or replace the Spindle.

DIFFICULTY: 7 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Main drive shaft is bent. Usually from a crash or blade strike.

LIKELIHOOD: 2 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Straighten or replace main gear and shaft.

DIFFICULTY: 6 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: One or both Paddles may be misaligned. Usually the result of a crash.

LIKELIHOOD: 3 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Align Paddles to zero pitch.

DIFFICULTY: 1 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Bent Flybar.

LIKELIHOOD: 4 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Straighten or replace the Flybar.

DIFFICULTY: 3 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: Too many head dampening shims installed.

LIKELIHOOD: 8 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Install an equal amount of head dampening shims on each side to remove axial play.

DIFFICULTY: 5 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

CAUSE: The Flybar may not be centered. Usually the result of a crash.

LIKELIHOOD: 9 on a scale of 1 to 20 where 1 is most likely and 20 is least likely.

REMEDY: Center the Flybar.

DIFFICULTY: 3 on a scale of 1 to 10 where 10 is most difficult and 1 is easiest.

Introduction

I purchased both parts from HeliWorld. They were delivered quickly and in good shape. I did not like paying over $11.00 for shipping from California to Wisconsin however. I suggest googling on the part numbers shown above and see if you can’t do better.

A lot of folks have switched out the stock, one-piece main gear and shaft for the Century brand main gear with auto-rotation capabilities, and separate main shaft. Let’s look at the positive side of doing this conversion:

The stock main shaft is notoriously soft and bends easily during minor crashes. The Century main shaft is reportedly constructed from a harder metal. I have no evidence to support or refute this.

It is much easier to replace the Century main shaft if it does get damaged.

The auto-rotation system allows you to perform auto-rotations. This is useful in the event of an in-flight main motor failure.

Replacing the Century main shaft is a couple bucks cheaper than replacing the stock main gear and shaft.

The Century main gear is known to spin truer. The stock main gears are usually out-of-round directly from the manufacturer.

During power down the main rotor will free-wheel which allows the main motor to stop spinning sooner resulting in less brush wear (OK that’s really reaching).

Modifying the Blade CP is fun!

OK – now let’s look at the negative aspects:

The Century main gear and shaft combo is slightly heavier than the stock one-piece gear/shaft assembly.

Some tinkering is needed to get the gears to align properly.

That’s all the negativity I can come up with. That’s a pretty good ratio of positive to negative.

All right – let’s modify this thing.

Remove the old parts

Remove the stock landing gear. If you have the Super landing gear, just move the battery tray all the way forward to allow the main gear and shaft assembly to be lowered out of the airframe.

Pull the Retaining Pin (035).

Loosen the Main Shaft Retaining Collar (047).

Pull the Main Shaft & Drive Gear (050) out through the bottom of the airframe. If the retaining pin hole on the main shaft is deformed, and they usually are, you will have to clean up any burrs with a suitable tool like a jeweler’s file (Figure 2). A burr here will cause the shaft to bind on the Center Hub (008), Swashplate Ball (043), Main Shaft Retaining Collar (047), and the Bearings (014) as you try to remove it. Resist the temptation to cut off the main shaft for quick removal – we’re going to need it intact in a subsequent step.

Prepare the new parts for installation

Notice that there are two holes in the new main shaft, one on either end (Figure 3). One hole is drilled nearer to the end of the shaft than the other. The hole that is nearer the shaft end is the bottom of the shaft. Take one of the two included short pins and insert it into the bottom shaft hole as shown in Figure 4. Make sure that equal amounts of pin protrude through each side of the shaft. Place a small drop of silicone oil or your favorite light oil into the auto-rotation mechanism and the outside of the bushing as shown in (Figure 5). Insert the bushing into the auto-rotation mechanism ensuring that the end with the groove is showing after installation (Figure 6). Insert the shaft into the bushing hole and slide it all the way up. Engage the pin into the bushing groove (Figure 7). The shaft should now rotate freely in one direction and not the other while holding the gear stationary.

There is a critical dimension that must be checked and maintained. Let’s do that now. (Figure 8) shows you how to measure the distance between the top of the gear and the retaining pin hole. Measure both the old main shaft and the new. This dimension should be identical. Mine was, and it measured in at 2 11/32 inches. If this dimension is not identical between the old and new assemblies, you will have to verify your neutral pitch settings.

Another thing that should be done now that will help you in the future is to measure the distance from the gear to the top of the main shaft on both assemblies, old and new. What the heck for you ask? Well, as you probably know, the swashplate is supposed to be set so that there is one-half inch of main shaft protrusion through the top of the swash when the controls are neutralized. The new shaft is shorter than the old one by 1/8 inch so you will need to subtract that from one-half inch and retain that number (3/8 inch) for future use when setting the swash up.

Installation

Make sure that the old shaft bearings are still installed and fully seated in the airframe.

Insert the new shaft and gear assembly up into the airframe from the bottom of the helicopter. Pass it through the bearings (014) and then install the new retaining collar. There is a step on both ends of the new retaining collar so it doesn’t matter which end goes against the bearing. If you choose to reuse the original Main Shaft Retaining Collar (047), make sure the tapered end goes against the Bearing (014). Continue to insert the shaft up through the Swashplate Ball (043) and Center Hub (008).

It’s interesting enough for me to mention that the new gear has an outside diameter of 2.79 inches while the old measures in at 2.75 inches. I thought that this must mean that the new gear has more teeth, but no, they both have 140 teeth. The spacing between teeth must be slightly different however. After much consideration I believe that there will be no effect on head speed but you will have to move the main motor over a bit in its adjustable range.

Make sure you have loosened the Main Motor Screws (027) and slid the motor over to allow for the slightly larger new gear. Now slide the main shaft with the new gear attached into position. Make sure it is fully seated against the bottom bearing and that the gears are properly meshed. Right about now you should be realizing that the 2 gears don’t align properly. The new main gear is significantly lower than the stock gear. I found this to be unacceptable and spent hours going over possible solutions. I tried removing the aluminum hub with autorotation mechanism from the plastic gear and installing it on the other side (henceforth referred to as “flipping the hub”) (Figure 9), but that just made the misalignment move to the other end of the pinion. A person could remove material from the top of the hub (many people have done this), but I eliminate this as a solution because I don’t want to make the retaining pin hole move up or down as it throws off the head settings.

Here is my list of solutions (along with my opinion of each):

Leave the hub installed as it comes from the manufacturer and live with the misalignment. (No good)

Flip the hub and live with the misalignment. (No good)

Leave the hub installed as it comes from the manufacturer and pull the pinion further out on the motor shaft. (No good)

Flip the hub and push the pinion further onto the motor shaft. (Acceptable)

Flip the hub, manufacture and install a shim of proper thickness between the motor and frame. (Acceptable)

I finally decided to go with flipping the hub and pushing the pinion further onto the motor shaft (Figure 10). This puts the main gear very close to the bottom of the airframe. I’m sure I will have to trim the canopy to keep the main gear from rubbing it.

The shim solution is just as good, but you may have to come up with longer Main Motor Screws (027). Also, the shim should cover the entire contact surface between frame and motor.

Using hand pressure only pinch the main gear up and the retaining collar down as you tighten the setscrew on the Main Shaft Retaining Collar (Figure 11). Some people recommend allowing a little vertical play here, but I say let the bearings do their job. You don’t want the main shaft spinning inside the bearing inner-race.

To properly set the gear mesh between the Main Motor pinion and the new main gear cut a small strip of common writing or printer paper. All you need is a strip about one-half inch by one inch. Place the strip of paper between the two gears where they mesh as shown in Figure 12. Pinch the two gears using firm hand pressure. The strip of paper should “crinkle” and conform to the shape of the gears as it is squeezed between the teeth. Tighten the two Main Motor Screws (027) securely. This sets the proper amount of play between the gears to prevent binding or slipping. To remove the paper simply rotate the main gear until it is free. Rotate the main gear slowly and observe the mesh between the gears. There should be the slightest amount of free play between the gears throughout an entire revolution of the main gear. Make sure that the new main gear does not contact any wiring or cable ties.

Align the hole near the top of the shaft with the Center Hub retaining pin hole, and insert the Retaining Pin (035). You’re allowed to swear and curse here as much as needed to get that pin in.

Put the landing gear back on or reposition the battery tray depending on what style gear you have.

If the previously mentioned “critical dimension” was the same on both the old and new shaft assembly, you’re good to go. Fire it up and go fly. If not you will need to setup the RC Helicopter Swashplate.

Summary

This is a very worthwhile modification for the money in my humble opinion. Again, look at the ratio of positives to negatives, more commonly referred to as a “risk to reward ratio” and you’ll see that this should be at the top of one’s mod list, especially for newer pilots. This is a 100% functional mod – no bling here at all. Thanks to all of the site members that have provided valuable input to these instructions by participating in our ever-growing user forum.

Parts Needed

Out with the old…

If you have a pitch gauge I recommend you take a neutral reading prior to the upgrade and then adjust the Pitch Control Links (006/007) to return to neutral after the upgrade.

Remove both Main Rotor Blades (042).

Disconnect Pitch Control Links (006/007) from the Blade Grips (037).

Disconnect both upper and lower ball connections on the Paddle Control Pushrods (009) and slide the Pushrods (009) over the Blade Grips (037) to remove them.

Using two 1.5mm hex wrenches remove one of the Blade Grip retaining screws (013) and then remove both Blade Grips, Spindle (016), O-rings (038) and Washers (015, 039 and 040). If you had Head Dampening Shims installed remove them too. If at all possible you should replace the O-rings (038) at this time also.

…and on with the new.

Disassemble the new upgrade kit and install two of the included Head Dampening Shims and an O-ring (038) onto the Spindle (016) as shown in Figure 2. Make sure that these parts have a light coat of silicone lube during assembly. This is especially important for the O-rings (038) to prevent “sticky collective”. Don’t forget that the step on Washer (015) always goes against the Blade Grip bearings.

Now install the other O-ring (038), shims and Washer (015) to the other end of the Spindle as shown in Figure 3.

Slide the other Blade Grip (037) onto the exposed Spindle (016). Do not push the O-rings (038) into the Center Hub (008) opening as this will diminish the dampening effect of the o-rings. Install the remaining Blade Grip retaining screw (013), but do not tighten. Before proceeding make sure that your Blade Grips are installed correctly as shown in Figure 4. When you are sure that the Grips are installed correctly tighten the Blade Grip retaining screws (013) using two 1.5mm hex wrenches.

The manufacturer suggests shortening the Pitch Control Links (006/007) 1-1/4 to 2-1/4 turns (depending on setup). Attach the adjustable Pitch Control Links (006/007) to the short end of the mixer arm first. Then attach the fixed-length control rods to the Upper Swashplate (044). Figure 5.

Reinstall the Paddle Control Pushrods (009).

Wrapping it up!

If you were not able to get an initial neutral reading with a pitch gauge then follow these instructions:

Set Main Blade pitch to zero.

Before proceeding you should unplug both Main and Tail motors from the 4-in-1, arm it and move the collective and cyclic through all ranges to check for binding. Correct any binding before continuing.

Check and adjust Main Rotor Blade tracking.

That’s it! You’re ready for a maintenance test flight.

This was a very easy upgrade to install. Follow these instructions carefully and you should have no problems.

When weather permits a flight I’ll report back how it differs from the stock head.

Heat Sink Installation

Strangely enough this was the most difficult part of the operation. I used the GWS EHS-12 heat sink with the GWS EDP-50/H motor. I ended up filing a small chamfer on the inner edge of the heat sink to get the motor started. I applied heat sink paste to the inside of the heat sink prior to installing. This heat sink was very difficult to get started on the motor. It is an extremely tight fit, which is great for a heat sink, but it was very difficult to get started. Brute force was the answer. I bent the capacitor out of the way (Figure 2) so I could get a good push on the back of the motor (Figure 3). Once I got the motor started inside the heat sink I supported the assembly on blocks as shown in Figure 4 and pushed the heat sink the rest of the way onto the motor.

Okay – that was difficult! The rest should be easy… Now I can’t (easily) rotate the heat sink into the proper position – it’s too tight on the motor can. After scratching my head for several minutes I finally got out the channel-locks and a protective strip of rubber. I CAREFULLY wrapped the motor in the rubber and gently grasped the motor can with the pliers. Figure 5. Notice that I grasp the motor at the shaft end so as not to deform the can. I only squeeze the pliers enough to prevent the motor from turning. Twist the heat sink into the position you desire. Figure 6 shows the orientation I used.

I recommend doing a water break-in on the new motor at this time.

Remove the old Tail Rotor Gearbox Housing

I tried using a debonder to dissolve the CA adhesive attaching the Tail Rotor Gearbox Housing (061) to the Tail Boom (056). I applied very small amounts with a toothpick as shown in Figure 7. I did this several times but the Gearbox remained tight on the Boom. I finally ended up using my dremel tool with a fine cut-off disc to carefully cut through both sides of the Tail Rotor Gearbox Housing (061) as shown in Figure 8. The Housing (061) can now be easily removed. Clean up the end of the Tail Boom (056) with fine sandpaper.

If you are in the process of performing this upgrade you may want to consider cutting off the Tail Boom (056) where it meets the Tail Rotor Gearbox Housing (061). The added weight of the bigger Tail Motor is difficult to offset by shifting the battery forward. A shorter Tail Boom prevents this. Regardless of which method you employ make sure you don’t damage the Tail Rotor electrical wires running through the Boom.

Install the Blade Adapter and Blade

Partially thread a setscrew into both sides of the Blade Adapter. Slip the Blade Adapter onto the Tail Motor output shaft. Using the provided hex wrench tighten the two setscrews evenly onto the shaft as shown in Figure 9.

Press the rubber bushing into the Tail Rotor Blade as shown in Figure 10. It is possible to install the bushing on the wrong side of the Tail Blade so use Figure 10 as a guide to putting it on correctly.

Insert the Tail Motor into the new Gearbox Housing as shown in Figure 11. Align the screw holes while ensuring that the heat sink does not contact any part of the Gearbox Housing. Figure 12. Install the retaining screws as shown in Figure 13.

Place a washer on the Blade Adapter and then thread the Tail Blade onto the Blade Adapter as shown in Figure 14. The hex wrench is used to prevent the motor from turning while threading the Blade Assembly onto the Adapter.

When the Blade Assembly is completely threaded onto the Adapter install a washer onto the Adapter and then the retaining nut. Tighten the blade retaining nut snugly but do not crush the rubber bushing. Figure 15. Use Loctite on the Adapter thread if possible.

Install the new Gearbox

Slide the new Tail Rotor Gearbox Housing onto the Tail Boom and route the wires to the motor. Carefully position the Gearbox Housing so that the tail motor is installed perpendicular to the Main Shaft (050). Figure 16. Don’t use the Tail fin as a reference – it is too flimsy and could be bent.

You have installed the blade correctly if it looks like Figure 17. Notice that when the tail blades are rotated until they are vertical, the top blade’s leading edge points forward.

Solder the leads onto the proper connection to give the correct rotation. Of course this can be changed by simply flipping over the tail motor connection at the 4-in-1 Controller.

The last step is to use a thin cyanoacrylate (CA) adhesive to attach the Gearbox Housing to the Tail Boom. I install the Housing and then apply just a drop of CA to the joint as shown in Figure 18.

A few last things…

Allow the CA to dry as indicated by the product’s label. After a short run-up recheck all screws and the retaining nut for security. It would be wise to check these also after the next couple of flights.

You will undoubtedly have to adjust the 4-in-1 Gain and Proportion settings.

Check the aircraft’s center-of-gravity (CG) as outlined in the owner’s manual. You will need to move your battery all the way forward. If moving your battery all the way forward still doesn’t provide the desired CG then consider cutting an inch off of the Tail Boom. I did not have to cut anything off of the Tail Boom.

And finally… was it worth the $22.98 (plus shipping). I think the answer is “Yes” in varying degrees depending on what type of flying you do and how well you do it. If you’re an experienced pilot you will love the tail authority available. A brand new guy who is still putting the tail in the dirt fairly frequently will probably be frustrated by this mod. Wait a month or two. For the people that are primarily hovering, you will notice a slight improvement in tail response.

Balancing the Main Rotor

I prefer to balance the entire Main rotor Assembly as a unit while it is removed from the aircraft.

Balancing must be done in a room where there is no air current from heating/cooling units, etc. or from people or objects moving around.

You must first remove the Flybar and Rotor Head Assembly and the Center Hub, Spindle and Blade Grip Assembly. These can be removed as a unit by disconnecting the Paddle Control Frame Pushrods (009) from the Upper Swashplate (044). Then remove the Retaining Pin (035). Now you can remove the entire Main Rotor Assembly from the aircraft by pulling the Center Hub (008) off of the Main Shaft (050).

I use a balancing device that I made from scrap wood. Figure 1.

Prior to balancing, prepare the Main Rotor Assembly by grasping each Main Blade Grip (037) in your hands and pulling them away from one another. Figure 2. This will force the head into the position it would most likely find during flight when centrifugal force acts upon it. Most Blade owners experience a certain amount of play in the Main Rotor Assembly as a result of the Spindle (016) length. To accommodate this play during balancing follow these instructions and pull the Blade Grips (037) outward.

Place the Main rotor Assembly in the balancing device as shown in Figure 3.

Place strips of tape on the light blade to achieve balance. I try to estimate the length of the tape needed and place it carefully on the light blade near the blade tip with the sticky side of the tape facing up. This way I can move the tape in or out until perfect balance is achieved. Then I flip the tape over and stick it to the light blade in the same spot it was when face up. I try to use a single piece of tape that will go from the trailing edge over the top and back underneath to the trailing edge again. This guarantees a smooth surface over the entire blade profile. Figure 4.

Continue to check and add or remove tape as needed to achieve balance.

Reinstall the Main Rotor Assembly, Install the Retaining Pin (035) and reattach the Paddle Control frame Pushrods (009) to the Upper Swashplate (044).

If you made any adjustments to the balance or are replacing blades, the track must be checked as outlined in the next section.

Setting Main Blade angle to zero

Another nominal setting that is beneficial under certain circumstances is Main Rotor Blade pitch set to zero degrees.

To accomplish this we must first unplug the Main and Tail Motors from the 4-in-1 Controller. Figure 5. Make sure that no battery is connected to the aircraft. Set the transmitter to the normal starting position as shown in Figure 6. Turn on the transmitter.

If you are certain that the Main and Tail Motors are disconnected from the 4-in-1 Controller, plug the battery into the aircraft and wait for the 4-in-1 to arm.

Stand clear of the aircraft and raise the throttle to 50%. Hopefully the Main and Tail Motors did not spin since they are to be unplugged from the 4-in-1.

Place the Idle Up switch in the Idle Up position (toward the face of the transmitter). Make sure that the collective/throttle is at 50%, cyclic is centered along with trim, throttle trim is in the down (off) position.

Now eye down the length of each blade comparing the bottom of the flat-bottom blade (042) to the top of the Paddle Control Frame (031). Figure 7. They should be parallel to one another. If you are using symmetrical blades use the blade centerline for comparison.

Lengthen or shorten the Pitch Control Links (006, 007) to obtain zero degrees (parallel to Paddle Control Frame).

A word to the wise: Whenever you make adjustments to the Pitch Control Links (006, 007) or the Servo Pushrod Control Links (045) make note of how many turns or half-turns you make to each. That way if you are not happy with the outcome you can always go back to where you started.

My experience has been that when starting from this point I usually need to lengthen the Pitch Control Links (045) 2 or 3 turns to achieve the proper throttle to hover ratio. I use the very crude measurement of ¾ throttle should have me hovering chest high on a fresh stock battery and 10T pinion with flat-bottom blades.

Tracking the Main Rotor

This operation requires that the Blade be run up at approximately 75% throttle. This is usually enough to cause the aircraft to lift into a hover. Therefore you must secure the aircraft against this. I just lay something heavy across the landing gear. Figure 8. The Tail Rotor will also spin during the Tracking operation. Be careful. I like to do this on a bench so that it is easier to observe the track.

Prepare the Main Rotor Blades (042) by coloring the tips in contrasting colors. I use a Sharpie brand magic-marker – one red and one black. Figure 9.

Prepare a “Tracking Flag” by folding a piece of standard writing paper in half along its length.

Prepare your transmitter by centering all of the trim sliders except for throttle which should be all the way off (down). Do this carefully – it’s important. Move the collective/throttle lever all the way down. Idle Up switch in the Normal mode. Figure 6. Make sure that no battery is connected to the aircraft. Turn on the transmitter. Plug in the battery and wait for the 4-in-1 to arm.

With the aircraft secured against lift-off and the Main and Tail Rotor areas clear, increase throttle to about 75%. Make sure that the aircraft is properly secured against movement. Hold the Tracking Flag in hand and slowly move it into the main rotor disc until the blades lightly contact the paper. Watch your fingers! Figure 10.

Reduce the throttle to zero and observe the red and black marks on the paper left from the blade tips.

If adjustment is needed, disconnect the battery and turn off the transmitter. Lengthen the Pitch Control Link (006, 007) of the low blade (the blade that made the lower mark on the paper). Do this in half-turn increments and re-check at 75% throttle. Continue until you have achieved the best track possible within the half-turn limitation of the Pitch Control Links.